1. Field of the Invention
This invention relates to a magnetic disk cartridge. This invention particularly relates to a magnetic disk cartridge comprising a small-diameter, very thin magnetic disk which is rotated at a high speed for recording and reproducing of image information or the like.
2. Description of the Prior Art
Floppy disks are widely used as recording media for computers because of easiness of handling and low costs. The floppy disk comprises a disk-like base made of a flexible polyester sheet or the like, and magnetic material layers overlaid on opposite surfaces of the disk-like base. The floppy disk is rotated at a high speed for magnetically recording information in the magnetic material layers by use of a magnetic head.
On the other hand, by utilizing the aforesaid advantages of the floppy disks and the advantages of a magnetic recording medium over silver halide photographic films that the magnetic recording medium can be reused, it has been proposed to use a magnetic disk having a size smaller than the size of the floppy disks as an image recording medium in still cameras. The magnetic disk used for still cameras comprises a small-diameter, very thin magnetic recording medium, and a hub secured to the center of the magnetic recording medium. The magnetic disk is rotatably housed in a small-size, hard case having a hub hole for exposing the hub of the magnetic disk at the center of the front surface of the case, and magnetic head insertion apertures for exposing a part of the magnetic disk in the front surface and the rear surface of the case. The combination of the magnetic disk and the case is called a magnetic disk cartridge.
When video signals are magnetically recorded by use of the aforesaid magnetic recording medium, since the frequency band of the video signals is very broad as compared with the frequency bands of digital signals and audio signals, the magnetic recording is conducted at a high recording density. Therefore, in the case where the magnetic layers for recording the signals therein have fine dust, small protrusions or recesses, flaws, peelings, or the like, the drop-out phenomenon in which the signals recorded are not reproduced correctly due to signal attenuation arises.
However, since the magnetic disk cartridge is usually carried and used outdoors, there is a risk of dust entering from the apertures of the cartridge for insertion of a magnetic head and clinging to the surfaces of the recording medium. Also, the portion of the recording medium exposed to the outside at the magnetic head insertion apertures is readily damaged due to contact with external materials.
To eliminate the above-described problems, the cartridge of the aforesaid type has heretofore been provided with shutter members for closing the magnetic head insertion apertures to protect the magnetic disk and opening the apertures at the recording and reproducing steps. Typicaly, the conventional shutter members are positioned between the case of the cartridge and the magnetic disk housed in the case, and rotatably supported on engagement portions positioned at the center of the case. The shutter members are engaged with one end portion of an elongated strip-like link member the other end portion of which is exposed to the outside of the case. When the link member is operated from outside of the case and moved, the shutter members are rotated by the link member to open or close the magnetic head insertion apertures. (In many cases, the shutter members are normally urged by an urging means in the closing direction, and rotated in the opening direction by the movement of the link member.)
The aforesaid link member must not come into contact with the magnetic disk housed in the case of the cartridge. Therefore, usually, a pair of guide grooves are extended in face-to-face relation to each other in the inner surfaces of upper and lower halves constituting the case. The upper and lower side edge portions of the link member are engaged with the guide grooves, and the link member is moved along the guide grooves. As described above, the link member is fabricated in the elongated strip-like shape so that the link member can be accommodated in a small space in the cartridge. However, since the link member has the elongated strip-like shape, it adversely affects the cartridge assembling efficiency. That is, when the cartridge is assembled, the lower side edge portion of the strip-like link member is first engaged with the guide groove of the lower half of the case positioned with the inner side facing up. Thus the link member is erected on the guide groove of the lower half. Then, the upper half of the case is mounted on the lower half from above the lower half so that the upper side edge portion of the link member is engaged with the guide groove of the upper half. In this manner, the link member is supported in the case. However, when the link member is erected on the guide groove of the lower half, the link member is readily disengaged from the guide groove even by small shocks.